Function transformFuncCall

src/backend/parser/parse_expr.c:1385–1428

}

static Node *
transformFuncCall(ParseState *pstate, FuncCall *fn)
{
	Node	   *last_srf = pstate->p_last_srf;
	List	   *targs;
	ListCell   *args;

	/* Transform the list of arguments ... */
	targs = NIL;
	foreach(args, fn->args)
	{
		targs = lappend(targs, transformExprRecurse(pstate,
													(Node *) lfirst(args)));
	}

	/*
	 * When WITHIN GROUP is used, we treat its ORDER BY expressions as
	 * additional arguments to the function, for purposes of function lookup
	 * and argument type coercion.  So, transform each such expression and add
	 * them to the targs list.  We don't explicitly mark where each argument
	 * came from, but ParseFuncOrColumn can tell what's what by reference to
	 * list_length(fn->agg_order).
	 */
	if (fn->agg_within_group)
	{
		Assert(fn->agg_order != NIL);
		foreach(args, fn->agg_order)
		{
			SortBy	   *arg = (SortBy *) lfirst(args);

			targs = lappend(targs, transformExpr(pstate, arg->node,
												 EXPR_KIND_ORDER_BY));
		}
	}

	/* ... and hand off to ParseFuncOrColumn */
	return ParseFuncOrColumn(pstate,
							 fn->funcname,
							 targs,
							 last_srf,
							 fn,
							 false,
							 fn->location);
}

/*
 * Check if this is CASE x WHEN IS NOT DISTINCT FROM y: